By using this system as an example it was shown that that grain boundary diffusivities, in nanostructured metals which had been prepared by means of severe plastic deformation at 398 to 448K, were 4 to 5 orders of magnitude higher than those in the same materials when in a coarse-grained state. The experimentally measured activation energy for grain-boundary diffusion was close to that for free surface diffusion; in spite of the absence of any residual porosity in the materials. The increase in diffusion permeability of interfaces, as observed for severely plastically deformed Ni relative to coarse-grained and nanostructured electrodeposited Ni, was attributed to a special non-equilibrium (high-energy) state of the grain boundaries in metals which were prepared by means of severe plastic deformation.

Grain Boundary Diffusion Characteristics of Nanostructured Nickel. Y.R.Kolobov, G.P.Grabovetskaya, M.B.Ivanov, A.P.Zhilyaev, R.Z.Valiev: Scripta Materialia, 2001, 44[6], 873–8